I noticed with my solar engines that color was very important. The side that collects the solar energy heats up much better if it is painted black. I am currently working on two identical pop can engine designs. The only difference between them is that one will be made of black Coke Zero cans, and the other will be made of silver Diet Coke cans. I am interested to see if the color makes any difference in a pop can engine. I am told that black works better to both absorb and radiate heat.

I have the pressure chambers and the displacers built. I will keep you posted on the final results. It is difficult to control all the variables, so it is not a very scientific experiment. But it is just as easy to make two of these as it is to make one!